Synthesis and herbicidal evaluation of novel benzothiazole derivatives as potential inhibitors of D1 protease.

D1 protease is a C-terminal processing protease that has been predicted to be an ideal herbicidal target. Three novel series of benzothiazole derivatives were synthesized and evaluated for their herbicidal activities against Brassica napus (rape) and Echinochloa crusgalli (barnyard grass). The preliminary bioassay indicated that most of the synthesized compounds possess promising D1 protease inhibitory activities and considerable herbicidal activities. Molecular docking was performed to position representative compounds into the active site of D1 protease to determine a probable binding model.

Facile and efficient synthesis and herbicidal activity determination of novel 1,2,4-triazolo[4,3-a]pyridin-3(2H)-one derivatives via microwave irradiation.

A series of novel 1,2,4-triazolo[4,3-a]pyridin-3(2H)-one derivatives were synthesized and identified by (1)H NMR, single crystal X-ray diffraction, elemental analysis or HRMS, and their herbicidal activities were determined at different concentrations. It was found that some of the title compounds possess high herbicidal activity. Furthermore, DFT calculation was used to study the SAR.

Synthesis and Herbicidal Activity of 5-Heterocycloxy-3-methyl-1-substituted-1H-pyrazoles.

With the objective of finding valuable herbicidal candidates, a series of new 5-heterocycloxy-3-methyl-1-substituted-1H-pyrazoles were synthesized and their herbicidal activities were evaluated. The bioassay results showed that some compounds exhibited excellent herbicidal activities at the concentration of 100 mg/L, and compound 5-chloro-2-((3-methyl-1-(2,2,2-trifluoroethyl)-1H-pyrazol-5-yl)oxy)pyrimidine showed bleaching activity to green weeds. In greenhouse conditions, this compound also showed excellent post-emergence herbicidal effect against Digitaria sanguinalis L. at the dosage of 750 g a. i. ha(-1).

Secondary Metabolites from Aspergillus sparsus NBERC_28952 and Their Herbicidal Activities.

Fungi have been used in the production of a wide range of biologically active metabolites, including potent herbicides. In the search for pesticides of natural origin, Aspergillus sparsus NBERC_28952, a fungal strain with herbicidal activity, was obtained. Chemical study of secondary metabolites from NBERC_28952 resulted in the isolation of three new asperugin analogues, named Aspersparin A-C (2-4), and a new azaphilone derivative, named Aspersparin D (5), together with two known compounds, Asperugin B (1) and sydonic acid (6). The structures of these compounds were elucidated based on extensive spectroscopic data and single-crystal X-ray diffraction analysis. All of the isolated compounds were evaluated for their herbicidal activities on seedlings of Echinochloa crusgalli and Amaranthus retroflexus through Petri dish bioassays. Among them, compounds 5 and 6 exhibited moderate inhibitory activities against the growth of the roots and shoots of E. crusgalli seedlings in a dose-dependent manner, while 6 showed obvious inhibitory effect on seedlings of A. retroflexus, with an inhibitory rate of 78.34% at a concentration of 200 µg/mL. These herbicidal metabolites represent a new source of compounds to control weeds.

Synthesis, Crystal Structure, Herbicidal Activity, and SAR Study of Novel N-(Arylmethoxy)-2-chloronicotinamides Derived from Nicotinic Acid.

Nicotinic acid, also known as niacin, is a natural product, which is widely found in plants and animals. To discover novel natural-product-based herbicides, a series of N-(arylmethoxy)-2-chloronicotinamides were designed and synthesized. Some of the new N-(arylmethoxy)-2-chloronicotinamides exhibited excellent herbicidal activity against Agrostis stolonifera (bentgrass) at 100 µM. Compound 5f (2-chloro-N-((3,4-dichlorobenzyl)oxy)nicotinamide) possessed excellent herbicidal activity against Lemna paucicostata (duckweed), with an IC50 value of 7.8 µM, whereas the commercial herbicides clomazone and propanil had values of 125 and 2 µM, respectively. The structure-activity relationships reported in this paper could be used for the development of new herbicides against monocotyledonous weeds.

Chemical components from the stems and leaves of Clausena lansium (Lour.) Skeels and their potential herbicidal effects.

BACKGROUND: Clausena lansium (Lour.) Skeels, belonging to the genus Clausena of the family Rutaceae, has a wide range of medical and agricultural activities. Previous studies on agricultural activities have shown that C. lansium extracts and some components have obvious herbicidal activities. In order to study systematically herbicidal activity of this plant, we studied the herbicidal effect of ethyl acetate (EtOAc) extract from the stems and leaves of this plant and further isolated the active compounds. RESULTS: The EtOAc extract inhibited the growth of roots and shoots of Echinochloa crus-galli (L.) Beauv., and the inhibitory effect of the EtOAc extract on roots were stronger than those on shoots with half maximal inhibitory concentration (IC50 ) values of 420.45 and 585.05 mg L-1 , respectively. Fifteen compounds were subsequently isolated and identified from the stems and leaves of C. lansium, including nine O-monoterpenoid furanocoumarins and six cinnamamides. Our results showed that most compounds exhibited varying degrees of herbicidal activities to E. crus-galli. Among them, compounds 3, 8, and 13-15 showed the best inhibitory activities on the growth of E. crus-galli roots, with inhibition rate values ranging from 70% to 83% at a concentration of 300 mg L-1 . Compounds 1 and 2 are two new compounds, and their structures were established as 5-O-monoterpenoid furanocoumarin and 8-O-monoterpenoid furanocoumarin, and named as claulansicoumarin-A and -B, respectively. CONCLUSION: The EtOAc extract and pure compounds showed noticeable herbicidal activities against E. crus-galli and indicated a great potential for these natural compounds to be developed as a herbicide. © 2020 Society of Chemical Industry.

Synthesis and herbicidal activity of novel pyrazole aromatic ketone analogs as HPPD inhibitor.

BACKGROUND: 4-Hydroxyphenylpyruvate dioxygenase (HPPD, EC 1.13.11.27) has been a good target for herbicide discovery. In order to discover novel HPPD herbicides, a series of pyrazole aromatic ketone analogs were designed and synthesized. RESULTS: The 25 pyrazole aromatic ketone analogs synthesized were tested for herbicidal activity and compounds A1, A3, A4, A17, A20 and A25 displayed excellent herbicidal activity against Chenopodium serotinum, Stellaria media and Brassica juncea at 37.5 g ha-1 . In addition, compounds A1, A5, A9, A10, A16, A17, A20 and A25 exhibited good crop selectivity for wheat, maize and rice at 150 g ha-1 . Inhibition activities against AtHPPD proved the compounds were HPPD inhibitors. The structure-activity relationship of these pyrazole aromatic ketone analogs was studied using molecular docking. CONCLUSION: These pyrazole aromatic ketone derivatives could be used as lead structures for development of HPPD herbicides against dicotyledonous weeds with further structure modification. © 2019 Society of Chemical Industry.

Design, synthesis and herbicidal evaluation of novel uracil derivatives containing an isoxazoline moiety.

BACKGROUND: Glyphosate is the most widely used and successful herbicide discovered to date, but its utility is now threatened by the occurrence of several glyphosate-resistant weed species. Saflufenacil is a relatively new herbicide developed by BASF in 2010. It is a highly effective selective herbicide showing excellent control on broadleaf weeds (more than 90 species), significantly superior to other protoporphyrinogen oxidase (PPO) inhibitor herbicides at the level of weeds controlled. It is also effective against glyphosate-resistant Conyza canadensis if used in combination with glyphosate. A series of novel uracil-based PPO inhibitors containing an isoxazoline moiety were designed via the intermediate derivatization method, synthesized using a key saflufenacil raw material as starting material and evaluated for herbicidal activity. RESULTS: The target compounds were characterized by 1 H NMR and high-resolution electrospray mass spectra. Bioassays indicated that some title compounds can control efficiently and effectively both broadleaf weeds and grassy weeds at low doses, especially the glyphosate-resistant weeds C. canadensis and Eleusine indica. CONCLUSION: This work provides a basis for further studies of 9b for control of a wider range of weeds, particularly for glyphosate-resistant weeds.

Herbicidal activity of pure compound isolated from rhizosphere inhabiting Aspergillus flavus.

In the quest for bioactive natural products of fungal origin, Aspergillus flavus was isolated from rhizosphere of Mentha piperita using Potato Dextrose Agar (PDA) and Czapec Yeast Broth (CYB) nutrient media for metabolites production. In total, three different metabolites were purified using HPLC/LCMS and the structures were established using 500 Varian NMR experiments. Further the isolated metabolites in different concentrations (10, 100, 1000 µg/mL) were tested for herbicidal activity using Completely Randomized design (CRD) against the seeds of Silybum marianum and Avena fatua which are major threats to wheat crop in Pakistan. Among the isolated metabolites, one compound was found active against the test weed species whose activity is reported in the present work. The chemical name of the compound is 2-(1, 4-dihydroxybutan-2-yl)-1, 3-dihydroxy-6, 8-dimethoxyanthracene-9, 10(4aH, 9aH)-dione with mass of 388. Results showed that all seeds germinated in control treatment; however, with the metabolite treated, the growth was retarded to different levels in all parts of the weeds. At a dose of 1000 µg/mL of the pure compound, 100% seeds of S. marianum and 60% seeds of A. fatua were inhibited. Interestingly, the pure compound exhibited less inhibition of 10% towards the seeds of common wheat (Triticum aestivum).

Design, synthesis and herbicidal evaluation of novel 4-(1H-pyrazol-1-yl)pyrimidine derivatives.

BACKGROUND: A series of novel pyrazolylpyrimidine derivatives were designed, synthesised and characterised by IR, (1) H NMR, (13) C NMR, mass spectroscopy and elemental analysis. The herbicidal activities of 30 pyrazolylpyrimidine derivatives were assessed. RESULTS: Nine compounds caused good herbicidal activity for Pennisetum alopecuroides L. Among them, N-ethyl-6-[5-methyl-3-(trifluoromethyl)-1H-pyrazol-1-yl]-pyrimidin-4-amine exhibited the strongest inhibitory activity against the root growth of P. alopecuroides, with an IC50 of 1.90 mg L(-1) . 2-Methyl-4-[5-methyl-3-(trifluoromethyl)-1H-pyrazol-1-yl]-6-(prop-2-yn-1-yloxy)pyrimidine produced the highest inhibition of chlorophyll level in seedlings of P. alopecuroides (IC50 = 3.14 mg L(-1) ). CONCLUSION: The structure-activity relationship indicated that the alkynyloxy group at the 6-position on the pyrimidine ring played a very important role for bleaching activities. When the alkynyloxy group was replaced by alkoxy, amino, alkylthio and alkylsulfonyl groups, the bleaching activities of the compounds were diminished. However, the compounds substituted by an amino at the 6-position of the pyrimidine ring exhibited excellent inhibition activities against weed root growth.

Synthesis, crystal structure, herbicidal activities and 3D-QSAR study of some novel 1,2,4-triazolo[4,3-a]pyridine derivatives.

BACKGROUND: 1,2,4-Triazolo[4,3-a]pyridine derivatives represent a new series of compounds that possess good herbicidal activity against Echinochloa crusgalli (L.) Beauv., Setaria faberii, Digitaria sanguinalis (L.) Scop., Brassica juncea Coss., Amaranthus retroflexus L. and Eclipta prostrata L. RESULTS: A total of 23 novel 1,2,4-triazolo[4,3-a]pyridine derivatives were synthesised and identified by (1) H NMR, IR, single-crystal X-ray diffraction, mass-spectroscopic and elemental analysis, and their herbicidal activities were tested against E. crusgalli (L.) Beauv., S. faberii, D. sanguinalis (L.) Scop., B. juncea Coss., A. retroflexus L. and E. prostrata L. at 150 g a.i. ha(-1) . It was found that the title compound 8-chloro-3-(4-propylphenyl)-[1,2,4]-triazolo[4,3-a]pyridine possesses high herbicidal activity and a broad spectrum against the 22 test weeds, with an inhibition effect of about 50% at a dosage of 37.5 g a.i. ha(-1) , and is safe for corn, cotton and rice at a dosage of 150 g a.i. ha(-1) . Furthermore, comparative molecular field analysis contour models were established to study the structure-activity relationship of the title compounds. CONCLUSION: It is possible that, with further structure modification, 1,2,4-triazolo[4,3-a]pyridine derivatives, which possess good herbicidal activities, may become novel lead compounds for the development of herbicides against dicotyledonous weeds.